In a conventional so-called intermediate roll-drive six-high rolling mill (hereinafter referred to as a six-high mill), the minimum value of the work roll diameter is determined by the flexural rigidity value of the work rolls, which withstands the tangential force of the intermediate roll drive, if there are no support rolls on portions of the work rolls inside and outside the rollable strip width of the work rolls. According to Non-Patent Document 1, for example, this value is 180 mm to 380 mm in the case of a 4-feet width material upon the intermediate roll drive.
A conventional six-high mill may have support rolls inside the rollable strip width of the work rolls. Further, a six-high mill, which has support bearings provided outside the rollable strip width of the work rolls, and applies horizontal bending to the work rolls via these support bearings, is disclosed in Patent Document 1.    Non-Patent Document 1: “Industrial Machinery”, May Issue, 1991 (pp. 56-60)    Patent Document 1: JP-A-5-50109